To write and read at high areal densities as used by modern tape systems, the magnetic tape has to be in close proximity to the read/write elements on a tape read/write head. Research efforts are spent to arrive at a viable solution to reduce the distance between the tape and the head, in operation, as reducing this spacing allows for increasing the areal density. The current technology typically requires a tape-head spacing of several tens of nanometers.
When a tape is streamed over a surface an air bearing forms, which prevents the tape from coming in close contact with the head. Thus, minimal tape-head distances cannot reach the nanometer-range. A solution that is typically used by current tape heads is to rely on skiving (i.e., sharp) edges to scrape off (skive off) the air. This forms a low pressure region directly after the skiving edge, such that the tape is pushed into intimate contact with the tape head, due to the higher air pressure on the opposite side of the tape. An advantage of this solution is that the tape-head spacing is small and stable over a wide range of tape speeds. A disadvantage is the friction and wear that arise due to the direct contact and the high pressure with which the tape is pushed into contact with the head. To prevent excessive friction, the tape can be intentionally made rough (i.e. with sporadic bumps on the tape surface so that only a fraction of the tape surface is in actual contact with the tape bearing surface of the head). Effectively, these bumps increase the tape-head spacing.
Now, to increase the linear density, one can seek to reduce the tape-head spacing by using a smoother tape. However, using a smoother tape results in an increased friction that can degrade the recording and read back performance of the tape drive. In extreme cases, friction can even cause the tape drive motors to stall and tape breakage.
In the related technical field of hard disk drives (HDDs), the magnetic medium is not in direct contact with the read/write head. There is an air bearing between the head and the disk. Because the disk is a rigid surface, the head can be pushed towards the disk to reduce the air bearing thickness such that the disk-head spacing is only a few nanometers, which can be compared with several tens of nanometers for tape media. The non-contact recording in an HDD virtually eliminates head wear, while operating at very small disk-head spacing.